Why is this happening? Green house gases from burning fuels are causing runaway warming on a global scale — and warmer temperatures melt the ice.

Greenland has been covered by ice for about three million years, and Antarctica has been covered for about eight million years. Latest estimates indicate that there are 680,000 cubic miles of ice on Greenland, which would raise the oceans by more than 20 feet if it were to melt completely.

Ian Joughin, Univ. of WashingtonThis is a view down the Ilulissat Fjord toward the terminus where Jakobshavn Isbrae rapidly discharges ice to the ocean. This fjord is frequently clogged with icebergs along its entire 60-km (37 mile) length.

Since 1998 there have been at least 79 estimates of the melting of ice sheets on Antarctica and Greenland, all of which have some flaws. These flaws include: only looking at certain regions, not studying the ice sheets over the long term, or only using one technique to measure ice loss, since each technique has their own flaws.

Andrew Shepherd from the University of Leeds in the UK and his colleagues complied data from 1992 to 2011 using satellites to measure changes in elevation, velocity of ice sheets, changes in gravity, and precipitation. Combing these methods carefully and overlapping time and geography from the different studies adds certainty to the measurements.

Their results show that since 1992 Antarctica has lost about 1,320 gigatons of ice and Greenland has lost 2,940 gigatons. This melt has contributed to 11 millimeters of sea level increase.

Previous estimates from 1958 to 2010 have been all over the map. Estimates of yearly mass change for Antarctica ranged between a loss of 246 gigatons and a gain of 27 gigatons. In Greenland annual estimates ranged from a loss of 308 gigatons to a gain of 10 gigatons.

Ian JoughinOver the course of several years, turbulent water overflow from a large melt lake carved this 60-foot deep canyon. Note the people for scale.

They noted that both of the polar ice sheets seem to be melting more rapidly than they thought from previous observations. Greenland is losing five times more mass today than it was in the early 1990's and Antarctica is losing 50 percent more ice.

Ian JoughinLarge melt lake that is just one of the many supraglacial lakes that form on the ice sheet's surface during the period of strong summer melt.

When asked what this meant for future melt, the researchers warned that any prediction they made now would be inaccurate because we can't be sure how much the Earth will warm. There are many variables adding to the ice melt and rising temperatures.

Even the Intergovernmental Panel on Climate Change has concluded they could no longer place limits as to how much ice melt will contribute to sea levels rising because the melting keeps increasing — the only thing the researchers know for sure is that ice sheets are definitely melting and sea levels are certainly rising.